Process for separating cyclopentene from piperylene



1 taining hydrocarbons of v tween carbon atoms,

desirable to isolate hydrocarbons by Patented May 28, 1946 '1' OFFICE 2,401,282 PROCESS FOR SEPARATING CYCLOPENTENE FROM PIPERYLENE Charles E. Welling, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application May 18, 1942, Serial No. 443,493

4 Claims.

This invention relates to a process for the separation of mixtures of olefins of diflerent types, or of olefins and paraiiins, containing five to seven carbon atom per molecule, into two or more portions having different properties or condifierent types. By olefin I refer to hydrocarbons containing at least One oleflnic linkage, that which may be described more specifically as mono-olefins, diolefins, or cyclic olefins. More particularly, this invention relates to the use of methanol in order to render separation into'hydrocarbon types by fractional distillation much more practical and feasible than by simple fractional distillation alone.

Hydrocarbon mixtures of a complex nature are producedin various petroleum cracking processes and in other ways. In order to best utilize certain components of such mixtures, it is frequently or recover these components in concentrated form. Thus, it is frequently desirable to utilize pentenes in a substantially concentrated form for the manufacture of pentadienes; similarly, it is desirable to separate the resulting pentadienes from the unreacted pentenes. Althoughno difiiculty is experienced in' preparing a hydrocarbon fraction by conventional fractional distillation that will have'a rela tively narrow boiling range and that will contain for the most part hydrocarbons having the same number of carbon atoms per molecule, further segregation of the hydrocarbons is difiicult if not impossible to achieve by ordinary fractionation.

There are a number of instances among the five-, six-, and seven-carbon olefin and paralfin hydrocarbons in which two or more hydrocarbons of different types are quite near-boiling. As commercially important instances may be mentioned the following:

Hydrocarbon Q E A. Pentene-2 (low-boiling isomer) 96.697.5 n-Pentane 97. Pentene-Z (high-boiling isomer) 98. 6

B. Piperylene (high-boiling isomer) 111.5 Cyclopentene 111. 6-112, 0

C. Hexene-2 (mixture of isomers). 154-156 n-Hexane l55. 8

In these examples of close-boiling hydrocarbons, it will be readily understood that the differences in boiling point within each example are too small for commercially feasible separations of the conventional fractionation.

Furthermore, certain cases exist in which hydrois a double bond be-v positions. A further object of my invention is to provide a method for separation by azeotropic distillation of five carbon atom hydrocarbons of different types, namely diolefins; and cyclo-olefins from mixtures of two or more of such hydrocarbon having relatively close boiling points, whereby one or more of the different hydrocarbons may be concentrated, or separated in sub stantially pure form. Another object of my invention is to provide an entraining agent for use in the distillation of such hydrocarbon mixtures to aid in the separation of the difierent hydrocarbons one from the other. A specific object of my invention is piperylene from a material containing the same and from each other.

My invention is a process for the separation,

and a mono-olefin that have like boiling points results in so changing the relative volatilities of the paraifin and mono-olefin that upon fractional distillation the overhead product is found to have a higher parafiin-mono-olefin ratio than the original mixture. Thus, although the addition of methanol to a pure paraffin or a pure mono-olefin results in the formation of a minimum-boiling azeotropic mixture in each case, there is in general a greater increase in the apparent volatility of the paraflin than in that of the mono-olefin. A similar eflfect is found for paraflins and diolefins, in that the addition of methanol results in a greater enhancement'of the volatility of parafiins than of that of diolefins. I have further found that the presence of methanol result in enhancing the relative volatility of mono-olefins and cyclo-olefins in comparison with that of dito separate cyclopentene and involved, however, so 1 column at some point alon fins is ordinarily remove olefins. Accordingly, itmay be said that in general the more saturated hydrocarbon is concentrated in the overhead product, and the less sat-- urated is concentrated in the kettle product. In this way, I may use methanol to separate likeboiling olefins, that i mono-olefins, diolefins. and/or cyclo-olefins, one from the other or from paraffins.

I may apply my process to a variety of hydrocarbon mixtures. In general I prefer to treat relatively narrow-boiling mixtures such as might result from a preliminary conventional fractional distillation. In order to obtain maximum efliciency in practicing my process of azeotropic distillation, it is desirable that the hydrocarbon mixture contain not more than minor amounts of hydrocarbons boiling more than about 4 to 6 F. above the olefin in the mixture that is to be produced as a kettle product. ,No such limitation is ar as the presence of hysiderably below the olefin d as a kettle product is drocarbons boiling can or oleflns to be produce concerned.

As will be understood by those skilled in the art, the many different ways of carrying out azetropic distillations which are known to the art may be applied with suitable modification, in view of this disclosure, to carry out the present invention. Thus, batchwise fractional distillation may be utilized in practicing my process, or continuous fractionation may be employed. In the latter case, the hydrocarbon mixture 15:1 was employed. Th

In operating my process, I use any convenient method of removing the methanol from the products of the fractionation, such as water washing. The methanol thus separated from the hydrocarbons may then be recovered.in known fashion such as by simple fractional distillation, and returned to the azeotrope column.

The pressure at which my process is most conveniently operated depends upon the volatility of the hydrocarbon mixture being distilled. Thus, in fractionating five-carbon hydrocarbon mixtures, pressures up to around pounds per square inch gauge are usually desirable, whereas in fractionating sixand seven-carbon hydrocarbon mixtures pressures near atmospheric are advantageously employed. However, if desired, pressures higher than thes may be used.

In order further to illustrate and describe my invention, I may cite the following examples, without, however, limiting the invention thereto.

EXAMPLE I A mixture of n-pentane and pentene-2 having a specific gravity (20/20) of 0.6361 and an estimated pentene-2 content of about 37 per cent, together with methanol in a hydrocarbon-tomethanol volume ratio of 200:155, was subiected to batchwise fractionation at atmospheric pressure in a column of 1.2-cm inside diameter packed to a height of 120 cm with {6-inch diameter single-tum wire helices A reflux ratio of about e course of the distillais continuously charged to the fractionating tion is shown in Table I.

TABLE I Pentene-2-N-pentane separation by azeotropic fractionation with meflumol Boiling range (ocr- Percent pentened rected to 760 mm.) Ent'mnu in v I t cumuL vol 8 in traction Fraction overhead g g g percent of up vol. percent g charge By a By B" F. 0. gr. firm titr.

(Methanol-free) 5-87. 1 30. 3-30. 5 l5. 0 l4. 0 14. 0 L 3600 87. 3 30. 6-30. 7 l1. 1 16. 0 30. 0 1. 3601 87. 3 30. 7 l3. 0 l3. 5 43. 6 1. 3606 87. 3 30. 7 l3. 5 16. 0 59. 5 1. 3616 3-88. 5 30. 7-31. 4 15. 0 l4. 0 73. 5 1.8693 588.9 31. 4-3L6 12.0 11.0 84.5 1.8785 15.6 100.0 l2

g the column, and

the methanol entraineris added at the same point or at some other point or points along the column. In such a continuous fractionation, a product comprising one or more oled from the kettle ofthe column, and an azetropic mixture of one or more other hydrocarbons with the methanol is taken of! the top of the column. The olefin; removed from the kettle may or may not contain substantial amounts of the methanol, depending upon the relative amounts of entrainer and hydrocarbon mixture charged to the column, and my p ess may be operated with any desired ratio of methanol to hydrocarbon mixture equal to or greater than a minimum ratio which will be determined by the amount of methanol req to form azeotropic mixtures with the hydrocarbon or hydrocarbons which are to be distilled overhead. If desired, minor proportions of w ter,

preferably less than about 5 per c times be used in the azeotrope column along with the entrainer to aid the selective action of the methanol.

ent, may someof fractions 1 and 6 (Table methanol by water washing.

Cottrell boiling point an- The boiling p ints I), after removal of were determined with a In this application of my invention, efllcient separation of the two types of hydrocarbons. paraillns and mono-olefins, was-realized in spite of the fact that only a minute difference in the boiling points of the hydrocarbons exists It is practically impossible to eflect a comparable ee'p-' oration by the methods of conventional from. tional distillation.

'nxAMPmn An extremely close-cut hexane-hexene fracected temperatures (760 tion, distilling at can mm. mercury) .of 153.! to 154.8 I". and containv11l.6 F. (corrected t 2,401,882 3 mg 50.4 mole per cent m'ono-cleflns by bromine pentene and 32 mole per cent of the high-boiling titration, was subjected together with a volume .isomer of piperylene. This latter fraction was of methanol equivalent to 139 volume per cent oi thensubjected to batchwise fractionation at atthe hydrocarbon charge, to batchwise fractionmospheric pressure in the presence or methanol ation at atmospheric pressure in the column described in Example I. A reflux ratio of about 70:1 was employed. The course of the distillation is shown in Table II.

TABLIII Hezene-N-fiexane separation amounting to 45 volume per cent carbon volume. The fra scribed in Example I was of 70:1 was employed.

of the hydroctionating column deused, and a reflux ratio The course 01' the azeoby aeeotropic fractionation with methanol Boiling range cor- Entrainer Per cent rooted to 100 115m.) 1% ogderv01. t $5 52 n p muss in e I 081] D 011 Fraction vol o i charge 2mm hm y 1 Exclusive of value :0: fraction 0. Since the original hexane-hexene cut contropic distillation with methanol is shown in tained 50 mole per cent olefins, it is seen from Table III. v I

Taste III azeotropic separation of cyclopentene from highboizing ripen/lane with methimol Boiling range (cor- P61 cent I rented to 700 mm.) @338 Vol. 3 gr high-boiling Fractlon I head, vol. 532 per cent 20/20 gg' wgg g I o 0. per cent of charge 8p. at. 20/20 (Methanol-free) v i 98. 2-99. 0 36. 8-37. 2 20 9. l 9. 1 0. 7665 20 99. 0-99. 2 37. 2-37. 3 17. 7 12. 7 21. 8 0. 7568 20 99.0-99.2 37. 2437.3 16.7 12.5 34.3 0.7562 21 99.0-99.2 37. 2-373 16.7 12.5 46.8 0.7554 22 99.0-99.2 37. 2-373 17.5 11.8 58.0 0.7542 23 99. 0-99. 5 37.2 37. 5 15. 7 17. 1 75. 7 0. 7468 32 99.5 37.5 16. 7 10.2 85.9 0.7019 88 14.1 100.0 17

Table II that more than h recovered in 96 By fractionation of the so-called light oils produced in pyrolysis of hydrocarbon gases, a fraction containing five-carbon hydrocarbons of order to.produce a fra had a specific gravity was composed of about 68 mole per cent cycloction distilling at 110.8 to U o 760 mm. mercury) that (20/20) of 0.7473 and that was contained in the 'iractionally distilling said mi It is seen from Tabl v cent of the high-boiling isomer of piperylene that hydrocarbon charge was recovered in fraction 7 in about 88 per cent purity.

Even higher purity may readily aration by ordinary means.

Because my invention may be practiced otherwise than as specifically shown herein, and bemany modifications and variations oi it will vious to those skilled inithe art, itshould not .be restricted except as specifically indicated in the appended claims.

claim:

l. The process of separatin e which comprises xture in the prese In that about 2s per ence of suflicient with at least a substantial proportion of the cyclopentene in said mixture, separating a minimum-boiling hydrocarbon-methanol azeotrope containing said cyclopentene concentrated therein as a low-boiling product, and separating a higher-boiling product containing said piperylene concentrated therein.

2. The process of separating into its components a narrow-boiling-range mixture comprising cyclopentene and the high-boiling isomer of piperylene which comprises fractionally distilling said mixture in the presence of sufiicient methanol to form an azeotrope with at least a substantial proportion of the cyclopentene in said mix-' ture, separating a minimum-boiling hydrocarhon-methanol azeotrope containing said cyclopentene concentrated therein as a low-boiling product, and separating a higher-boiling product methanol to form an azeotrope' lo by the presence of water containing said piperylene concentrated therein. 20

3. A process for recovering concentrates of oyclopentene and of piperylene from an unsaturated hydrocarbon oil containing the same which comprises subjecting said oil to fractional distillation to produce a substantially constant-boiling mixture essentially comprising cyclopentene and piperylene, and fractionally distilling said mixture in the presence of at least sufflcient methanol to form anazeotrope with all of said cyclopentene to concentrate said cyclopentene in an overhead fraction as a minimum-boiling azeotrope with methanol and to concentrate said piperylene in the residue.

4. The process of claim 1 further characterized during said fractional distillation in an amount less than about five per cent of said methanol but sufficient to aid the selective action of said methanol.

CHARLES E. WELUNG. 

